fix #817

finding an optimal nest for a large list > 12 or so starts to take a
noticeable long time - O(n^2) scaling. The bulk of the time was in
`find_all_segment_splits`.

_backtrack is refactored so that permutations function is no longer
needed and we prune most of the search tree.

Project.toml

@@ -5,7 +5,6 @@ version = "1.0.50"
 
 [deps]
 CSTParser = "00ebfdb7-1f24-5e51-bd34-a7502290713f"
-Combinatorics = "861a8166-3701-5b0c-9a16-15d98fcdc6aa"
 CommonMark = "a80b9123-70ca-4bc0-993e-6e3bcb318db6"
 DataStructures = "864edb3b-99cc-5e75-8d2d-829cb0a9cfe8"
 Glob = "c27321d9-0574-5035-807b-f59d2c89b15c"
@@ -15,7 +14,6 @@ Tokenize = "0796e94c-ce3b-5d07-9a54-7f471281c624"
 
 [compat]
 CSTParser = "^3.4.0"
-Combinatorics = "1"
 CommonMark = "0.5, 0.6, 0.7, 0.8"
 DataStructures = "0.17, 0.18"
 Glob = "1.3"

src/JuliaFormatter.jl

@@ -11,7 +11,6 @@ using Pkg.TOML: parsefile
 using Glob
 import CommonMark: block_modifier
 import Base: get, pairs
-using Combinatorics: permutations
 using CommonMark:
     AdmonitionRule,
     CodeBlock,

src/nest_utils.jl

@@ -175,8 +175,9 @@ function nest_if_over_margin!(
     return false
 end
 
-function find_all_segment_splits(n::Int, k::Int)
+function find_all_segment_splits2(n::Int, k::Int, max_margin::Int)
     res = Vector{Int}[]
+    # n = size(dp, 1)
 
     if n == k
         return [fill(1, k)]
@@ -190,25 +191,23 @@ function find_all_segment_splits(n::Int, k::Int)
                 push!(res, t)
             end
             return
+        elseif current_sum >= n
+            return
         end
 
-        start_val = isempty(t) ? 1 : last(t)
-        max_val = n - current_sum - (k - length(t) - 1)
+        start_val = 1
+        max_val = n - k + 1
 
         for i in start_val:min(n, max_val)
             _backtrack([t; i], current_sum + i)
         end
     end
-    _backtrack(Int[], 0)
 
-    all_splits = Vector{Int}[]
-    for r in res
-        for c in unique(permutations(r))
-            push!(all_splits, c)
-        end
+    for i in 1:(n - k + 1)
+        _backtrack([i], i)
     end
 
-    return all_splits
+    return res
 end
 
 """
@@ -285,7 +284,7 @@ function find_optimal_nest_placeholders(
         end
     end
 
-    # @info "" dp placeholder_inds
+    @info "" dp placeholder_inds
 
     N = size(dp, 1)
 
@@ -307,7 +306,7 @@ function find_optimal_nest_placeholders(
             ranges
         end
 
-        all_splits = find_all_segment_splits(N, s)
+        @time all_splits = find_all_segment_splits(N, s, max_margin)
 
         best_split = UnitRange{Int}[]
         min_diff = 1_000_000 # big number!
@@ -330,6 +329,7 @@ function find_optimal_nest_placeholders(
     segments = Tuple{Int,Int}[]
     for s in 1:N
         segments = find_best_segments(s)
+        @info "" segments
         fits = true
         for (i, s) in enumerate(segments)
             if i == 1